Cosmic flux unit of steradians.

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Cosmic flux unit of steradians.

Post by wilsoncloud » Sun Feb 24, 2013 3:23 pm

Hello people,
I just found some answers through Google which linked to this interesting forum. I will take a look.
I found this post concerning the cosmic ray flux wrote by Chelle :
A good overview graph showing the cosmic ray flux as a function of energy can be found here:

Look at the first plot on the right. It shows a graph of flux, measured in number of particles per square meter per second per steradian per GeV (10^9 eV), on the vertical axis, versus particle energy, in electron volts, on the horizontal axis. You will see that the largest flux is at low energy (about 10^9 eV), where the flux is about 1000 particles/m^2-s-sr-GeV. That is, in one square meter, looking over the whole upper half of the sky (2 pi = 6.2 sr), in a bandwidth of 1 GeV, one sees 1000 particles every second.
I would like to know, if the flux is 1000 particles/m^2-s-sr-GeV and the "upper half of the sky" is 6.2 sr, so why the flux of particle won't be 6200 particles/m^2-s-GeV per "upper half of the sky" ?

In the fantastic book "The Particle Odyssey A Journey to the Heart of Matter" they says :
Roughly 20 ‘primary’ cosmic rays per square centimetre arrive each second at the top of the atmosphere.
I'm trying to find this flux (20 particles per cm²/s) with the cosmic ray spectrum, but it's not convincing. Anyone can help me ?
Thanks a lot,


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Re: Cosmic flux unit of steradians.

Post by chelle » Sat Mar 01, 2014 11:34 pm

Hi Wilson,

Welcome to the forum.

To be honest I don't understand your question and/or motivation very well.

Anyway perhaps these papers on cosmic rays might help, those links have been already posted before, but perhaps you've missed them:

- ... 0725v1.pdf


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